1. Field of the Invention
The invention relates generally to valve bags and, more specifically, the invention relates to valve sleeves used to fill and seal valve bags, such as shipping sacks that are used to contain and transport granular products (e.g., fertilizer, cement, animal feeds, or grains).
2. Description of Related Technology
Flexible bags such as paper shipping sacks may include sealable sleeves placed in the filling valves. A sealable sleeve provides a convenient means to and securely close the flexible bag to prevent the contents of the bag from leaking or sifting out of the bag. Sleeves may be constructed of polyethylene tubing or of paper, for example.
A typical paper sleeve for a paper shipping sack (such as a pasted valve type multiwall shipping sack) is made from a rectangular sheet of kraft paper that is rolled into a cylindrical shape and secured in the cylindrical shape by overlapping and gluing opposing edges of the sheet of paper to one another, forming a lapped seam. Such a sleeve is typically mounted to an opening, called a valve or filling aperture, located in a corner of the bag, that is used to allow introduction of the product that is to be held within the bag. This arrangement has been used even in more advanced shipping sacks that include a thermoplastic film liner adhered to the inner surface of the sleeve valve. In order to seal the paper sleeve and therefore the valve or filling aperture after the shipping sack is full, heat is applied to the thermoplastic film liner near an exterior end of the sleeve valve to secure the contents within the shipping sack. Sealing is typically accomplished using conduction heating, pressure, microwave energy, or ultrasonic application.
However, due to the double thickness of paper formed by the overlapping edges of paper forming the lapped seam of the sleeve, a gap is often present in the vicinity of the lapped seam of the sleeve after sealing, due to the discontinuity in the thickness of the sleeve at the edge of the paper that is disposed on the interior surface of the lapped seam. The discontinuity in the thickness of the sleeve impedes sealing and makes it possible for the contents of the bag to leak or sift out of the bag even after the valve has been sealed.